Modern theodolites as described, for example, in the printed publication "Prospekt, Vermessungsinstrumente, Leica AG, Liste G1 916d, Schweiz 1993" [Brochure, Measuring instruments, Leica AG, List G1 916d, Switzerland 1993] are distinguished by a high setting precision in the horizontal and vertical directions. Depending on the precision class of the respective theodolite, it is possible, in this case, to achieve standard deviations of up to 0.3". This corresponds to a setting precision of &lt;0.2 millimeter at a distance of 100 meters.
It becomes clear from this example that these precisions can be achieved only by an extremely high outlay on precision mechanics. In order to ensure this, a transition has been made to equip the manually controlled positioning drive, which is a rotating knob as a rule, with an encoder. The encoder signals are used to drive a setting motor. The manual alignment of the theodolite is therefore no longer done by a purely precision-mechanical gear, but by using a combination having electronic and mechanical drive elements.
Such drives have proven themselves in practice. However, vibrations and twisting movements are transmitted to the theodolite when the rotating knob is actuated. Exact sighting of the target is rendered difficult by such vibrations and twisting movements, particularly in the case of theodolites of the highest precision class.
The problems identified are not intended to be exhaustive but are among the many that reduce the precision of theodolites. Other problems may also exist. However, those presented above should be sufficient to demonstrate that currently known solutions are amenable to worthwhile improvement.